The invention relates to the control of an air-conditioning system in a motor vehicle, which has an automatic clutch. The vehicle engine, especially an internal combustion engine, is or can be connected to driven wheels of the vehicle via a gearbox. The gearbox can be changed over arbitrarily by the driver between drive positions and idle (isolation of gearbox input and gearbox output) and via the clutch arranged between the engine and gearbox. An actuator unit that operates the clutch assumes a self-adjusting starting position when the clutch is engaged and assumes an operating position with (slow) temperature drift when the clutch is disengaged.
Motor vehicles having automatic clutches of this type are produced on a large scale. The temperature drift of the actuator unit operated by the control can be neglected in all operating conditions in which the clutch is disengaged only for a more or less short time. This is the case when gears or drive positions of the gearbox are changed. The clutch also regularly assumes a disengaged state for only a short time when the vehicle is being driven off.
If sensors are provided in order to monitor the actual state of the clutch, it is therefore possible to dispense with complicated arrangements, which are also capable of registering the temperature drift.
If the gearbox is changed to idle, the clutch per se needs to be disengaged only during the change operation. As soon as the idling position of the gearbox has been reached, the clutch can be engaged again since, because of the isolation of the drive between the gearbox input and gearbox output which is present during idling, there is no drive connection between the engine and the driven wheels of the vehicle, and the engine can therefore continue to run in any desired way.
However, in the case of automatic clutches according to German Patent document DE 44 26 260 A1, provision is regularly made to leave the automatic clutch disengaged during idling. This is advantageous since, as a result, the risk of exciting noise in the gearbox, so-called gearbox rattling, during idling is considerably reduced.
Idling may be maintained over a relatively long time, so that the temperature drift of the actuator unit, which occurs when the clutch is disengaged, cannot be neglected. Therefore, German Patent document DE 44 26 260 A1 provides for the clutch, which is normally disengaged during idling, to be engaged temporarily for a short time at predefined intervals in order to reset the temperature drift.
The object of the invention is to ensure optimum control in the case of an air-conditioning system driven by the vehicle engine. According to the invention, this object is achieved by temporarily switching off the air-conditioning system driven by the engine when, during idling, the clutch is engaged temporarily in order to eliminate the temperature drift of the actuator unit.
The invention takes into account the novel finding that, during idling of the gearbox, a particular risk of exciting noise can occur if the input side of the gearbox is coupled in drive terms to the engine by engaging the clutch with the air-conditioning system switched on.
Since, during idling, the clutch is engaged for only an extremely short time in each case in order to compensate for the temperature drift, it is then virtually impossible to incur any losses in the output from the air-conditioning system as a result of switching off the air-conditioning system for a similarly short time. Instead, the comfort of the vehicle is increased considerably as a result of the reliable avoidance of noise.
Otherwise, with regard to preferred features of the invention, reference is made to the claims and to the following explanation of the drawing, using which particularly preferred embodiments of the invention will be described.